1. Field of the Invention
The present invention relates generally to a method and apparatus for the self-sustaining pyrolysis of waste materials. More particularly, the invention relates to a novel continuous method and apparatus for controllably removing moisture from the waste material using a portion of the heat of combustion of waste materials being pyrolyzed with the pyrolysis portion of the apparatus. Once the apparatus is at operating temperature it becomes self-sustaining and will dry and subsequently pyrolyze the waste material without the need for an external source of fuel.
2. Discussion of the Prior Art
The search for new energy sources has become increasingly important due to the rapid rate of depletion of existing fossil fuels. One of the more promising sources of new energy is waste materials presently being discarded or destroyed. By techniques of pyrolytic decomposition, many types of waste materials can be converted into energy rich fuels such as combustible gases and char, or fuel carbon.
In the past, several types of devices for pyrolyzing refuse and other waste products have been suggested. Many of these devices have proved unworkable or economically unfeasible. Others, while feasible in concept have been proved to be inefficient and unreliable in continuous operation. Still others, while attractive in theory, have been shown to be too expensive to manufacture, install and operate.
Among the most successful prior art refuse conversion devices are the devices described in U.S. Pat. Nos. 2,886,122; 2,993,843; 3,020,212; 3,098,458; and 4,205,613. The present invention constitutes an improvement upon certain of the devices described in these patents.
As will become apparent from the description which follows, several important improvements to the apparatus described in the aforementioned patents have been made. One of the major improvements involves the provision of a cooperatively associated moisture reduction apparatus for controllably pre-drying the waste material prior to its introduction into the pyrolysis unit. By pre-treating the waste material prior to pyrolysis significantly greater pyrolysis efficiencies are obtained resulting in the production of substantial quantities of produced, or by-product gases which can be used not only to sustain the operation of the apparatus but also to provide excess fuel for operating auxilliary devices such as electrical generators and the like. Additionally, by pre-treating the waste materials the recovery of useful by-products such as char, metal and organic liquids is substantially enhanced.
One of the major drawbacks of prior art systems for the pyrolytic destruction of waste materials, including municipal refuse, concerns their inability to efficiently and consistently pyrolyse materials having widely varying moisture content. Depending upon weather conditions and a myriad of other factors the moisture content of the feed material may vary considerably. If the material to be pyrolyzed has too high a moisture content the pyrolysis may be incomplete or marginal thereby adversely affecting the production of by-product produced gas. Similarly waste having varying moisture content causes undesirable variations in the other by-product materials produced such as char by-products which may be subsequently activated or gasified.
The unique apparatus of the present invention solves the problems of prior art pyrolyzing devices by providing cooperating means for controllably pre-treating and pre-drying the waste materials to be introduced into the pyrolysis chamber.
As will become apparent from the paragraphs which follow, the novel apparatus of the present invention, due to its unique design, efficiently uses the surplus heat of combustion of the waste material to accomplish the waste pre-treatment. The pre-treatment chamber of the apparatus is uniquely arranged to prevent contamination and rotates within a housing, the interior of which is heated by the surplus heat from the pyrolysis chamber. The rotatable pre-treatment chamber is mounted above the pyrolysis unit and is inclined so that the transfer of the waste material through the system is economically accomplished by force of gravity. Unique positioning means locate the pre-treatment chamber and function to prevent axial movement of the chamber within its housing due to the inclination of its longitudinal axis of rotation.
Both the pre-treatment chamber and the pyrolysis chamber are provided with fixed waste inlet and outlet passageways and cooperate to prevent heat loss to preclude atmospheric contamination and to ensure complete and efficient pyrolysis.